Radium-radon-actinium systematic in geothermal groundwater: constraints for groundwater upwelling-time in the Euganean geothermal field (Italy)

The Euganean Geothermal Field (EGF) extends on a plain band of 36 km² in the north eastern Italy nearVenice. Thermal waters (65°C to 86°C) are exploited from about 250 wells for a total flow rate of 17 Mm³/y.The Euganean thermal waters are of meteoric origin and infiltrate 80 km to the north of the EGF in the Venetopre-Alps. The geothermal reservoir is situated at a depth of 3 km in Mesozoic carbonate formations, whilethe regional Schio-Vicenza fault system and its permeable damage zone enhance the thermal fluid flow in thesubsurface. In the EGF area, the hot waters intercept an interaction zone between faults of the fault systemand rise quickly to the surface through the local fracture mesh. In order to constraint the upwelling timeof this thermal water from the deep reservoir, an isotopic study on stable (oxygen, hydrogen, carbon) andradioactive isotopes (radium, radon, actinium) has been carried out. In this paper we will report on the resultsof the radioactive isotopes.